entity framework 5 MaxLength

Question

I was using EF4 and a piece of code I found to get the MaxLength value from an entity like this:

public static int? GetMaxLength(string entityTy         


        

Answer 1

This is a very handy piece of code. I refactored it a bit and it's so useful I thought I would post it here.

public static int? GetMaxLength(Expression> column)
    {
        int? result = null;
        using (var context = new EfContext())
        {
            var entType = typeof(T);
            var columnName = ((MemberExpression) column.Body).Member.Name;

            var objectContext = ((IObjectContextAdapter) context).ObjectContext;
            var test = objectContext.MetadataWorkspace.GetItems(DataSpace.CSpace);

            if(test == null)
                return null;

            var q = test
                .Where(m => m.BuiltInTypeKind == BuiltInTypeKind.EntityType)
                .SelectMany(meta => ((EntityType) meta).Properties
                .Where(p => p.Name == columnName && p.TypeUsage.EdmType.Name == "String"));

            var queryResult = q.Where(p =>
                                          {
                                              var match = p.DeclaringType.Name == entType.Name;
                                              if (!match)
                                                  match = entType.Name == p.DeclaringType.Name;

                                              return match;

                                          })
                .Select(sel => sel.TypeUsage.Facets["MaxLength"].Value)
                .ToList();

            if (queryResult.Any())
                result = Convert.ToInt32(queryResult.First());

            return result;
        }
    }

And you can call it like:

GetMaxLength(x => x.CustomerName);

This is assuming you've got a DbSet defined in your DbContext of type Customer, which has a property of CustomerName with a defined MaxLength.

This is very helpful for things like creating Model attributes that set a textbox's maxlength to the max length of the field in the database, always ensuring the two are the same.